Traditional plastics do not biodegrade. Of course plastic breaks, tears and cracks. It weathers and sunlight makes it brittle, It falls apart – it degrades – but only into smaller pieces of plastic. And that can take hundreds of years. See Why Plastic Doesn’t Rot.

Plastic litter is not surprisingly increasing exponentially with disastrous environmental consequences.

But suppose there was a way of making non-biodegradable plastic, biodegradable? The plastic industry argue that they can do just that by means of chemical adatives known as degradation initiators.

Types Of Degradable Plastics

The ISO (International Organization for Standardization) has defined six types of degradable plastics.

• Degradable – breaks down in some way.
• Photodegradable, broken down by light
• Oxidatively degradable broken down by oxygen.
• Hydrolytically degradable. Broken down by water
• *Biodegradable – can be broken down by microbes to mass, water and co2 but with no indication of how long that might take. May also need chemical addatives to make this process possible.
• *Compostable – degrade at a rate that’s similar to other types of compostable materials, and they result, again, in water, carbon dioxide, humus, and inorganic compounds. Compostable plastics biodegrade naturally.They do not need additonal addatives to break down the polymers as they made from natural materials that microorganisms recognise.

This is a confusing list because the last two (*) seem to refer to the natural process of biodegrading while the others refer to  plastic with added degradation initiators. It is important to note that there is a huge difference. Degradable does not mean biodegradable despite what the plastics industry tries to imply.

What Are Degradation Initiators

Degradation initiators are added to the plastic mix in amounts of up to 2% of the total composition. Very basically, these addatives break the long unnatural plastic polymers into shorter recognisable polymers that microbes can attack and digest – or biodegrade.

English: illustration of the Oxo-Bio-Degradation is, as the name describes, a two-step process whereby the conventional polyolefin plastic is first oxo-degraded to short-chain oxygenated molecules (typically 2-4 months exposed) and then biodegraded by the micro-organisms (Bacteria, Fungi, etc.). (Photo credit: Wikipedia)

The process happens as follows.

• Microbes are attracted to the additive;
• They “crack” the long polymer allowing acces to other microbes and water.
• Eventually these will break down huge polymers into smaller and smaller bits.
• These smaller bits are then vulnerableto other microbes.

More Research

That’s the theory and it sounds good BUT as Green Plastics point out

“you can add an additive to normal, petroleum-based plastic that will make it become brittle and crumble in sunlight: this is referred to as making “photodegradable” plastic. Other additives can be put into plastic that will make plastic break down by oxidation: this is referred to as making “oxo-degradable plastic.”

These methods will make the bulk of the plastic appear to disappear; however, the small pieces (or even find “sand”) that is produced by this effect is still small pieces of plastic.  Nothing has changed. Over a matter of years, it is possible for the pieces to become small enough to be assimilated by microorganisms, but there is still a lot of research that needs to be done to verify how long this might take.  In the mean time, they are just very small pieces of plastic.”

Or this by Eco Savvy

“The only difference between “oxo-biodegradable” plastic and petroleum based plastic is the presence of an oxo-formulated additive in concentrations of 1-3% (metal salts) within the petroleum based plastic.  This additive allows the petroleum based plastics to degrade in the presence of oxygen, light, heat and moisture.

Oxo-biodegradable plastic is designed to degrade in the open environment and this short timeframe of biodegradation is not necessary. Furthermore, a high rate of conversion is not desirable because the conversion to greenhouse gases such as carbon dioxide contribute to the warming of the atmosphere, hole in the ozone layer and depletion of carbon available for the soil.”

The Right Place At The Right Time

The difficulty is of course ensuring that the plastic doesn’t start biodegrading in normal conditions so that the strength of the plastic product is not jeopodised. Biodegradation is designed to start in certain extreme conditions.

As 75% ofplastic ends up in landfill, most addatives are designed to work in landfill conditions.

While products may start to degrade outside of  the specified conditions but the process will take much longer.

The obvious flaw in this solution is the wrong product in the wrong place. For example plastic that has been manipulated to degrade quickly in a landfill conditions ending up as litter on the roadside where it will not degrade quickly.

Other Considerations

So, to become degradable, plastic has to be further chemically engineered. Obviously, this is by no means a natural process (as biodegrading is normally understood to be), rather it requires complex chemical eginerring.

The composition of these chemical addatives is secret and known only to the companies who produce them.

Biodegradable plastics are made using traditional (usually petrochemical based) plastics. They don’t always break down into harmless substances.

Confusing & Misleading Marketing

Because the initiators are bio-based this has led to the process being described as bio degradable. .

Which has led to confusion because now bio -degradable plastic could be a compostable plastic that biodegrades naturally OR plastic that has had a degradation initiator added to make it bio-degrade.

Compostable plastic is a plastic that can biodegrade with out chemical addatives within a certain amount of time.

The Guardian reported in October 2014 that

Last month, the FTC sent warning letters to 15 additional marketers, informing them that their claims “may be deceptive”. The FTC also requested “competent and reliable scientific evidence proving that their bags will biodegrade as advertised”. This time, the term of offense is “oxodegradable”, implying the bag will break down in time when exposed to oxygen.

And

“The plastic is not degrading, it’s fragmenting,” Greene said. Over time, as opposed to breaking down into less hazardous organic components, these plastic products break down into lots of small, equally toxic bits.

Why make plastics degradable?

Why go to the effort of making degradable plastic bags when we already have naturally compostable products such as paper bags and cornstarch bags. Why not use plastic for things we don’t want to rot away like drainpipes and use naturally biodegrading materials for disposable packaging?

Useful stuff to know

Degradable, biodegradable or compostable plastics – whats in a name
Why leaves rot and why most plastics don’t at Why Plastic Doesnt Rot

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